A membrane switch is generally utilized for an application wherein a light force is applied to an indicator to make an electrical contact which in turn controls certain selected electrical circuitry. The general construction of a membrane switch includes a base which has a plurality of conductors mounted on the base. A flexible sheet with a plurality of flexible conductors on one side of the sheet is mounted in alignment and spaced from the base. Selected portions of the flexible conductors on the flexible sheet are aligned with selected portions of the conductors on the base. Accordingly, the application of a force to the flexible sheet at a selected point moves an associated conductor toward an aligned conductor on the base until the conductors contact each other to complete an electrical circuit. The customary method of keeping the flexible sheet spaced a selected distance from the base sheet is to provide a spacer sheet having a selected thickness. The spacer sheet has apertures formed therein to allow selected portions of the flexible sheet to contact selected portions of the conductors on the base through respective apertures. An indicator sheet carrying indicia is mounted on the flexible sheet in alignment with the apertures to provide indicia which acts as a target for an operator applying a force to the flexible sheet.
A typical construction of a membrane switch of this general type is disclosed in U.S. Pat. No. 3,591,749 to James Martin Comstock, which patent is entitled Printed Circuit Keyboard. The Comstock disclosure teaches a membrane switch which has the broad basic construction described above and includes a transparent sheet for protecting the indicia which is positioned for indicating points for application of flexing force.
It is appreciated that membrane switches are utilized in applications were a force is applied to a flexible sheet to distend the sheet through an aperture and then contact the sheet on the other side. The flexible sheet has a conductor mounted thereon and this conductor must also be distended. Not only must it be distended, but it must also adhere to the sheet and not flake off or brake off even after many flexures of the sheet.
Ordinarily, membrane switches are used in applications were the voltage applied between opposite sides is low and the amperage is also low. In certain applications, it is desirable to provide a conductor on a flexible sheet which has a minimum amount of resistance but still may be made relatively inexpensively. Various materials are known to be used as conductors, and an obvious conductor is gold which is taught in U.S. Pat. Nos. 4,066,852, 4,066,853, 4,066,854 and 4,066,855 to George Edward Zenk. U.S. Pat. No. 4,085,302 to Zenk et al also discloses a gold film which is used in a membrane switch. U.S. Pat. No. 4,035,593 to James P. Riniker entitled Flexible Pressure Sensitive Switch Actuator Module Adaptable to a Keyboard Surface Having Fixed Contact Array teaches the use of silver film material. U.S. Pat. No. 4,154,178 to Jack Brown et al entitled High Density Programming Means for Programmable Sewing Machine teaches the use of berryllium copper having a layer of 2 mils thickness. U.S. Pat. No. 4,143,253 to Wagner et al entitled Optically Clear Membrane Switch teaches conductors having layers of copper, nickel and gold. The prior art teaches the utilization of a plurality of layers of conductive material in order to provide conductors having a minimum of resistance.